Furnace for electrolytic purposes



Nov. 17, 1936. L. FERRAND FURNACE FOR ELECTROLYTIC PURPOSES 4 Sheets-Sheet 1 Filed Dec. 3, 1934 f Fe rvah 9/.

Nov. 17, 1936. FERRAND 2,061,146

FURNACE FOR ELECTROLYTIC PURPOSES Filed Dec. 3, 1934 4 Sheets-Sheet 2 NOV. 17, 1936. FERRAND 2,061,146

FURNACE FOR ELECTROLYTIC PURPOSES Filed D60. 3, 1934 4 Sheets-Sheet 3 ,2 frr-anal pvvevmy Nov. 17, 1936. L. FERRAND 2,061,146

FURNACE FOR ELECTROLYTIC PURPOSES Filed Dec. 3, 1934 4 Sheets-Sheet 4 Pi g] Patented Nov. 17, 1936 UNITED STATES PATENT OFFICE Application December 3, 1934, Serial No. 755,836 In France February 24, 1934 11 Claims.

This invention rel...tes to furnaces for electrolytical purposes of the kind which comprises elec trodes swingably hung above a stationary hearth.

Such furnaces having an electrode which is not immersed in the material and which are heated by the are have been proposed in which a vertical electrode was slightly moved from time to time about its axis of suspension in order to allow each time a new charge of initial material being dropped at a place on the hearth.

This invention has for its object a different arrangement characterized in that said electrodes, which are arranged horizontally in a manner known per se, have a swaying motion continuously imparted thereto by a driving mechanism. This continuous oscillation allows to obtain a more extended and approximately uniform distribution of the electric energy in the furnace.

When the furnace is used for electrolytical 2 purposes, the lines of current between the immersed surface of the oscillating electrodes and the horizontal surface of the hearth continuously vary in position and length; for a suitable angle of oscillation, it is possible to obtain by this means at every point of the hearth a density of current the average value of which is approximately the same for all the points of the hearth.

The uniformity of distribution of the elementary currents is moreover improved when the axes of oscillation of the electrodes are continuously lifted and lowered by means of electromagnetic devices controlled by the intensity and voltage of the current passing through each electrode, so that the median axis of the lower face of this electrode, when a furnace for electrolytical purposes is under consideration, remains at a nearly constant distance from the hearth notwithstanding its movement of oscillation.

When the furnace is used for electrolytical purposes, the continuous oscillation of the electrodes also procures other important technical effects and particularly in that a regular operation may be attained more readily than by merely stirring up the materials according to the present practice with the aid of a pricker or by a rotational movement of the electrodes.

It is well known that the anode effect is a phenomenon which occurs most frequently in furnaces for dry electrolytical processes, and particu- 5 larly in electrolytic furnaces for the production of aluminum, same being taken as an example of application in the following.

Said phenomenon is evidenced by a sudden and most considerable increase in the electrical re- 5 sistance which results in a marked elevation of the tension at the terminals of the electrolytic set. The furnace then is said to be racing" or burning. This entails a sudden variation in the working of the generators, which brings about certain difliculties and inconveniences; 5 moreover, secondary electrolytic reactions take place in the melt which entail a decomposition of 'the same and which in addition are detrimental to the efficiency, the life of the furnace, etc. The method most commonly used to correct this 1 consists in stirring up the melt with the aid of a pricker, a manual operation which is attended with many inconveniences and which consequently it is advisable to avoid.

The mechanism of said phenomenon seems to 15 be due to the formation of large-sized gas bubbles which adhere to the bottom face of the anode, to the decrease in the capacity for said anode to be wetted by the melt under the influence of dust particles or of certain compolmds of electrolytical origin, to the decrease in the alumina content, etc.

It is well known that stirring up the melt brings said phenomenon to an end. The pricking" operation is comparatively easy in the case of 25 an electrolytic furnace of very small size, but with the present high-capacity furnaces it is a. most toilsome one to the works, and as a result the latter do not always perform it in time; moreover, the wear of the pricker by its con- 30 tact with the melt introduces iron into the metal; last, such practice is incompatible with the use of a tightly closed furnace.

Certain small-size sets have been designed with a view to secure the desired stirring up mechan- 5 ically; in the one the anode was arranged to revolve about its vertical axis; in the others the pan containing the melt was the revolving element. However, said methods apparently are not applicable easily to the present big-size elec 40 trolytical furnaces, and this brought the petitioner to find out a new, more practical and advantageous solution to the problem.

By virtue of the swaying motion of the electrodes which is maintained continuously by a 45 suitable mechanical device the bottom portion thereof is moved within the melt so that their faces on which gas bubbles are liable to form will assume such variable inclinations that said bubbles can escape easily. They come to burst out at the surface of the melt which remains liquid by reason of the agitation and also of the heat radiated by the crown.

The result of doing away with the anode effect is that the electrical working of the generator and the operation of the electrolytic oven become perfectly regular, which results in a higher current eiilciency and a better utilization of the initial materials. Such secondary reactions as are due to the excess voltage attending the anode effect are also done away with, whereby the cryolite consumption, an important element of the cost of aluminum, is decreased considerably or even suppressed. On the other hand, the equal distribution of the current over the hearth increases the life of the latter considerably and it is also adapted to increase the efiiciency of the electrolysis.

The use of tightly closed furnaces is particularly advantageous not only because the heat radiation from the crown maintains the melt surface in the liquid state and thus facilitates the gas evolution but also because it allows of maintaining a neutral atmosphere above the materials and'electrodes'and thus to collect the gases generated. Such tight closing of the furnace is not ea compatible with the use of horizontal oscillating electrodes on account of the necessity to shift their axes of suspension vertically for the purpose of taking up the wear thereof and adjusting the flow of current in a manner known per se,

above all where the furnace crown is to be left,

completely free.

The invention has for 'a secondary object mounting arrangements for the electrode-carrying shafts in the furnace walls whereby the possibility of adjusting the drive of said shafts is obtained while the desired tightness is secured.

It also contemplates the production of a. longitudinal movement of the electrodes in unison with the oscillatory motion of the same with a view to avoid the formation of solidified melt crusts at the ends thereof and to facilitate the escape of the bubbles from below the electrodes.

It also comprises particular arrangements concerning the furnace crown structure and means to discharge the initial materials gradually from a container located above said crown through the apertures therein as well as other peculiarities which are to be described with reference to the drawings appended hereto by way of example.

Figure 1 shows an embodiment of a furnace according to the invention drawn partlyv as an elevational view and partly as a vertical cross sectional view.

Figure 2 is a similar view taken transversely to i the former.

Figures 3 and 4 show details of a movable electrode and a block of the conducive hearth respectively.

Figure 5 is a horizontal cross sectional view taken on the axis of omillation of a supporting device arranged to lead the current to the movable electrodes.

Figure 6 is a diagram indicating the electric flow between the hearth and the electrodes by the time when the tilt of the latter is a maximum.

Figure 7 is a tic view of a distributing device for the hydraulic motors which control the rocking of the electrodes.

The furnace as shown, which is more particularly intended for the production of aluminum by electrolysis, comprises a closed laboratory I above a conducive hearth composed of assembled amorphous carbon blocks I laid upon a floor 3 made of refractory materials, the number and dimensions of said blocks being variable depending on the capacity of the furnace. Formed in the bottom face of said blocks is a groove 4 rectangular in section with bevels at the corners thereof (Fig. 4) which allows a cast steel tubing current lead 8 to be retained therein by means of a cast iron seal 5; said lead having a grooved outer face for better adhesion and a smooth inner face.

At either suitably machined and copper-plated end of said tubular member the connection with the current input cables I (Fig. 2) is secured by a gunmetal sleeve 8 comprising two halves clamped together through keyed bolts.

The side walls of the laboratory pan comprise a series of linings, viz, from the inside toward the outside:-at 9 of amorphous carbon, at Ill of carbon paste, at H of fire bricks, at l2 of kieselguhr bricks, at l3 of red bricks. Said pan is surrounded by a frame l4 composed of assembled shapes, insulated from the negative pole, strengthening the whole structure and providing a liquid-seal to receive the bottom portion of a semi-stationary casing i5 square in section.

Said casing, which has a twin wall filled with glass wool or like suitable heat-insulating substance, rests freely in the fluid-seal. Cut in the side walls of said casing are rectangular apertures It provided with vertical guides ll (Fig. 5) designed for graphited heat-resisting grease lubrication. Adapted to slide in said guides is a block l8 supporting the anode set from which it is electrically insulated by means of an insulating socket 20 of the tube is bent into a U-like shape (Fig. 2) c and is sealed by means of a cast iron seal within a groove 24 provided in the top face'of the respective electrode 25 (Fig. 3).

Each tube end I9 is rockably received in the related block I! (Fig. 5) and carries a driven pinion 25 meshing with a vertical rack 21; the latter is rigid with the rod of a hydraulic piston operating within a cylinder 28 the water intake and discharge cocks of which are controlled by a counterweight device of conventional type.

This distribution can be eifected for instance as diagrammatically indicated in Fig. 7. To the ends of each cylinder 28 are connected inlet conduits 45 and 41 and exhaust conduits 48 and 49. The conduits 46 of all the cylinders are connected to a common inlet conduit 50, all the conduits 41 are likewise connected to an inlet conduit 5|, and the conduits 48, 49 are connected to common exhaust conduits 52 and 53, respectively.

These conduits 50, 5|, 52, 53, as well as the two main conduits 54, 55, lead to the periphery of a valve box 55 which is rigid y secured to the support I80 and in which can rotate a cylindrical slide valve 51 having two notches 58, 59 allowing to cause conduits 50, 5| to alternately communicate with the conduit 54 connected to a source of fluid under pressure, and the conduits 52, 53 to alternately communicate with the discharge conduit 55.

To the rotary slide valve 51 is connected an arm 50 so arranged as to be engaged by abutments Si, 52 secured on a cable 63 attached to the rack 21 of one of the devices causing the electrodes to rock, this cable passing on rollers 64, '65 mounted on the respective panel l8 and being stretched by a counterweight 56. The abutments BI, 52 are adapted to rock the arm 6|! every time the piston 61 of said device reaches the end of its stroke, and

to thus compel the slide valve 51 to reverse the distribution.

- In the position indicated, the fluid under pressure passes through 54, 58, 50 and 46 in each cylinder 23. underneath the piston 61 and causes the latter to rise, whilst the fluid delivered by this piston escapes through 49, 53, 59 and 55. At the end of the upward stroke of the piston 61 and of the rack 21, the abutment 6| engages with the arm 60 and causes the slide valve 51 to rotate so that the notches 58, 59 cause 54 to communicate with 5| and 55 with 52, respectively; the fluid under pressure will then come above the piston, and the latter will be compelled to move down.

The amplitude of the reciprocating movement thus imparted to all the pistons 6'! at the same time depends on the position of the abutments 6|, 62 on the cable 63, which position can be adjusted at will, and the speed of oscillation depends on the degree of opening of the exhaust cook 55:: fitted in the pipe 55.

The piping 46 to 55 should include flexible portions in order to lend themselves to the relative displacements of the cylinders 28 in the vertical direction.

Said cylinder is hung to the block by a rigid bar I so that the displacements of the block will not modify the position of the cylinder with respect to the system comprising the piston, rack 21, pinion 26, shaft I9, 20 and electrode 25.

The upward and downward movements of the rack 21 which take place as long as water under pressure is admitted into the cylinder 28 cause the tube i9, 20, I9 to rock together with the anode 25 secured thereto.

The feed of water is simultaneous in all the cylinders, so that all the electrodes will oscillate in unison and with the same amplitude. As a whole they provide a conducive plane which sways above the hearth while remaining horizontal as a whole and the various portions of which take considerable inclinations in alternated directions.

The efiect of such swaying motion the amplitude and frequency of which can be adjusted as desired is continuously to stir up the fused salt charge and to secure its permanent homogeneousness as a result also of the fact that the feed of alumina is continuous.-

It follows moreover that the anode effect is completely suppressed and that a substantially equal distribution of the current over the hearth is obtained.

The flow of the electric current between the hearth 2 and the anodes 25 by the time of their maximum inclination is shown diagrammatically in Fig. 6. The lines of current AB are at right angles to the surfaces of the electrodes; the current intensity at each point is inversely proportional to the length of said lines of current; it is shown at the bottom of Fig. 6 by the ordinates a-b comprised between axis X-X and curve cc1cz which relates to anode 250 or curve dd1d2 which relates to anode 25d, and so forth. The maximum deflection of the electrodes (21 at either side of the vertical plane in the example shown) is so chosen that the flow issuing therefrom be tangent to the vertical plane through the axis of suspension of the next anode as clearly shown in Fig. 6. It will be appreciated that the hearth portion M-N between the two said vertical planes is swept over successively by the flow from anode 25d and that from anode 250, so that the average current intensity through each point is represented by the average of the ordinates of the two curve portions d-d1 and c1-cz and remains substantially constant.

The adjustment of the portion I! with a view to obtain both a correct tightening and the slimement of the bolt holes in box 2| can be eifected easily with the aid of a hand wheel 29 and a screw cap 2Ia.

By reason of the thread cut on sections is the.oscillation of the tube and the anode carried thereby is attended with a slight longitudinal reciprocating motion of the whole. Obviously, it would be easy to obtain a longer stroke if such should be considered as necessary either by using quick-pitch threads or by any other suitable method.

The effect of the longitudinal movement of the anodes is to prevent the formation of solidifled melt crusts at the ends thereof and to facilitate the escape of the gas bubbles from below the same.

A bracing 30 is provided to stiffen the U- shaped bar 20 and thus to make the tube system l92l||8 more rigid.

The latter moreover may be cooled by a water circulation, which causes a protective layer to form about the immersed portion of the tube by solidification of the melt, and which also prevents the overheating of the contacts.

The tube and anode structure is carried at either side of the furnace by one end 3|, insulated from said tube, of a vertical rod controlled by an adjusting mechanism 32 mounted on the casing and which may be driven if so desired by means of a reduction driving set 4| in relation with the electric constants of the furnace to be controlled.

A perfectly equal distribution of the current amongst the anodes is thus obtained. The contact brushesas a whole may be set under the influence of a tension-regulating voltmetric device.

The tubes 6 sunk in the carbon blocks of the hearth serve not only to lead in and distribute the current which is to flow through the melt of initial materials but also if desired to house heating or cooling means for the hearth, e. g. an electrical resistance 43 through which there flows a regulatable electric current or a hot or cold fluid (air, gas, etc.) circulated by any suitable means with a view to control the electric power of the furnace as desired.

The crown 33 of the laboratory is independent of the casing and pan; it consists of a kind of a twin walled bell filled with a suitable heat-insulating material the ceiling of which is strengthened by a system of angle iron girders 34 providing a frame. Arranged above said crown is a closed rectangular casing 35 which constitutes the alumina storage container. The foot of the crown and that of the casing rest respectively in packing channels 36, 31 fllled with alumina and carried by the pan and the casing respectively.

Apertures or chutes 38, 39 provided in the crown 33 serve to drop alumina into the laboratory and to let out the gases evolved therein to be taken away through a pipe 40.

A valve provided with a fllter (not shown) allows the air to escape without losses of material where same is handled pneumatically.

The alumina may be distributed through the chutes 38 e. g. by means of sheet iron plates or strips 45 slidably arranged on the ceiling of crown 33 and reciprocated in valve-like fashion so as altematingly to open and close small oriflces located in the axis of said chutes; said plates may be operated by means of rods 44 and links 42 driven by shafts b carrying eccentrics a or in any other suitable manner.

Crown 33 and casing 35 are not absolutely indispensable for the operation of the furnace. The effect of the crown is to considerably lessen the heat losses by radiation. If same is dispensed with the thermal efficiency will be less but the productive capacity may be greater.

Consequently, this furnace type is connected with a great flexibility in use which may be of great advantage in certain industries.

It will be understood that the constructional details described above and shown may be varied and that the various essential and secondary arrangements of the furnace selected as an example may be substituted by any other similar or equivalent arrangements with a view to adapt the furnace to the various purposes to which it may be applied without thereby departing from the scope of the invention.

For instance, where an aluminum refining process is contemplated, it would be only necessary that the electrodes consist alternatingly of soluble raw metal anodes and refined pure metal cathodes working in a suitable melt but without a conducive hearth. r

I claim:

1. A furnace for electrolytic purposes, comprising a stationary hearth, a plurality of horizontal movable electrodes, and means for causing each of these electrodes to continuously oscillate about and under a horizontal axis.

2. A furnace for electrolytic purposes comprising a stationary hearth, a plurality of horizontal movable electrodes and means for causing each of these electrodes to oscillate about and under a horizontal axis, the amplitude of the oscillations being such that gaseous bubbles can easily escape from underneath the electrodes when the latter are immersed in materials in molten condition.

3. A furnace for electrolytic purposes comprising a stationary hearth, a plurality of horizontal movable electrodes, and means for imparting to each of these electrodes both a movement of oscillation about and under a horizontal axis and a reciprocating movement parallel to this axis.

4. In a furnace for electrolytic purposes, the combination of a hearth composed of carbon blocks, metal tubes passing through these blocks, and a metal seal surrounding each of these tubes and in contact both with said tubes and with said carbon blocks, this combination being characterized by the fact that the tubes are made of steel and are arranged in a groove provided in the lower part of the carbon blocks, and that their seal is constituted by pig iron.

5. A furnace for electrolytic purposes comprising a stationary hearth, a plurality of horizontal shafts carried above said hearth, horizontal electrodes hung to said shafts respectively, a pinion on each shaft, a rack meshing with said pinion and a hydraulic prime mover imparting a reciprocating motion to said rack.

6. A furnace for electrolytic purposes comprising a stationary hearth, a plurality of horizontal shafts carried above said hearth, horizontal electhe related block, driving means to impart a rotary alternating motion to each shaft and means to raise and sink said shafts with the related blocks.

'7. In a furnace for electrolytic purposes the combination of a shaft made of three tubular sections detachably assembled endwise the mean,

section of which has a crank-brace shape, bearings supporting the ends of said shaft in horizontal alinement and a horizontal electrode rigidly secured to the mean section of said shaft.

8. In a furnace for electrolytic purposes, the combination of a shaft having its mean section shaped in crank-brace fashion, bearings supporting the ends of said shaft, at least one of said ends and the related bearing having a screwed engagement and means to impart an alternating rotary motion to said shaft, the effect of said screwed engagement being to compel the shaft to move to and fro longitudinally within the bearings.

9. An oven for electrolytic purposes comprising a laboratory, a semi-stationary casing the wall of which has an inverted L-shaped section and surrounding the space above the laboratory, the upper side of said wall being directed inward and its vertical side resting tightly on the periphery of the laboratory, a crown housed freely within said wall and the feet of which rest on the inner periphery of the laboratory, a casing secured on the top of the crown and designed to contain materials to be fused, the periphery of said casing resting tightly on the top of the semi-stationary casing, the crown having apertures therein which open in said casing and distribution means movable on thetop of the crown and adapted to allow dropping said materials in small amounts through said apertures into the laboratory.

10. In a furnace for electrolytic purposes, the combination of a shaft composed of three portions placed end to end, the middle portion having the shape of a crank shaft and the end portions being in alignment with the ends of this middle portion, two boxes adapted to assemble said portions one to the other, each of these boxes comprising two parts adapted to fit one against the other, a screw-threaded collar screwed on one of said parts and bolts connecting this collar to the other part and an electrode rigidly secured to the middle portion of said shaft.

11. In a furnace for electrolytic purposes, the combination of a vat, vertical slides placed on two opposite sides of the vat, a shaft the ends of which are guided by said slides, an electrode rigidly secured to this shaft and extending downwardly, means for imparting ato-and-fro rotary movement to said shaft, and means for supporting the ends of said shaft at variable levels.

I LOUIS FERRAND. 

